1. Field of the Invention
The present invention relates to a catalyst warming-up control device for quickly warming up a catalyst.
2. Description of Related Art
Conventionally, a catalyst is provided in an exhaust passage of a vehicle mounted with an engine. The catalyst has the optimum temperature for purifying exhaust gas. Warming-up of the catalyst is performed using the exhaust gas when the temperature of the catalyst is lower than the temperature high enough to purify the exhaust gas, for example, soon after the engine is started.
There is a known construction that is provided with a heat exchanger of a heat recovery device in an exhaust passage to recover exhaust gas heat. The exhaust gas heat recovered through the heat exchanger is used for heating or for increasing temperature of an engine coolant, for example.
As for a relative positional relationship between the catalyst and the heat exchanger in the exhaust passage, there can be a construction that arranges the heat exchanger upstream of the catalyst. In this case, the recovery of the exhaust gas heat is performed in the heat exchanger before in the catalyst. Therefore, this construction can increase the recovered amount of the exhaust gas heat more than the construction that arranges the heat exchanger downstream of the catalyst, for example, when quick temperature increase of the coolant is required. For increasing the recovered amount of the exhaust gas heat as compared to the construction that arranges the heat exchanger downstream of the catalyst, a construction that arranges the heat exchanger at the same position as the catalyst can be also employed.
However, in the construction that arranges the heat exchanger at the same position as the catalyst or upstream of the catalyst as described above, the recovery of the exhaust gas heat is performed in the heat exchanger before in the catalyst. Therefore, there is a concern that the warming-up of the catalyst using the exhaust gas heat delays. In this regard, for example, Patent document 1 (JP-A-H11-218020) describes a construction that provides a bypass passage upstream of the catalyst for preventing the exhaust gas from flowing through the heat exchanger and that switches the flow of the exhaust gas between the heat exchanger side and the bypass passage side with a passage switching valve. Thus, the construction prioritizes either the warming-up of the catalyst or the recovery of the exhaust gas heat.
However, in the construction described in Patent document 1, the bypass passage and the passage switching valve are indispensable components, so restrictions are imposed on the construction of the exhaust passage.